1. Field of the Invention
The present invention relates to improved threaded closure assemblies for containers. The invention also provides improved threaded closure caps.
2. Description of the Related Art
Current commercially mass-produced beverage containers use threads on the container neck and closure of the continuous, helical type. The threads comprise a single, substantially continuous thread portion on the container neck with a low thread pitch angle, typically less than 5°. The low pitch angle is needed in order to ensure that the closure does not unscrew spontaneously. The low pitch angle also provides the necessary leverage to achieve an air tight compressive seal between the closure and the container neck when the closure is tightened onto the container neck. The low pitch of the helical threads also means that the closure typically needs to be rotated through more than 360° to disengage it completely from the container neck.
Drawbacks of these low pitch helical threads include the laborious rotation required to remove and resecure the closure on the neck, excessive use of molding material to form the long helical threads, and unreliable separation of tamper-evident rings from the closure skirt due to the low pitch angle of the threads.
The present applicant has described an improved pressure safety closure for carbonated beverage containers in International Patent application WO95/05322. This application describes container closure assemblies having substantially continuous threads defining a substantially continuous helical thread path, although the pitch of the helix can vary. The closure can be moved from a fully disengaged to a fully secured position on the container neck by rotation through 360° or less. The threads on the neck or the closure are provided with mutually engageable elements to block or restrict rotation of the closure in an unscrewing direction beyond an intermediate position when the closure is under an axial pressure in a direction emerging from the container neck, the neck and closure being constructed and arranged to provide a vent for venting gas from the container neck at least when the closure is in the intermediate position. This pressure safety feature prevents the closure from blowing off uncontrollably once unscrewing of the closure from the container neck has started. It thus allows the use of shorter, more steeply pitched or multiple-start threads in the container and closure assembly, thereby rendering the assembly much more elderly- and child-friendly without sacrificing pressure safety. WO97/21602 and WO99/19228 describe improved versions of the assemblies of WO95/05322.
The beverage container closure assemblies exemplified in WO95/05322 have short projecting thread segments on the cap and longer projecting thread segments on the container neck. This arrangement is conventional, in part because of the requirements of high-speed injection molding of the caps, according to which the caps must be “bumped” off a (preferably) one-piece mold mandrel with minimum distortion.
Interestingly, the various screw-top formats for beverage containers have not yet completely replaced glass bottles with crown closures. This is despite the fact that crown closures require a bottle opener to open, and cannot be resecured on the bottle neck in airtight fashion, thereby making it necessary to consume the whole contents of such a bottle immediately after opening.
The present applicant considers that one of the reasons for the continued use of crown closures is that they are better suited for consumption directly from the bottle because the relatively smooth surfaces of the bottle neck are more comfortable between the consumer's lips. This characteristic will be referred to as the “user-friendliness” of the bottle neck. In contrast, screw top container necks have neck threads that present a relatively rough or abrasive surface to the lips.
It is an object of the present invention to provide improved screw top closure assemblies for containers. The present invention is especially applicable to beverage containers, including carbonated beverage containers.